1. Field of the Invention
The present invention provides anaerobic adhesive compositions, reaction products of which demonstrate controlled-strength at ambient temperature conditions and enhanced resistance to thermal degradation at elevated temperature conditions. The compositions are (meth)acrylate- and/or polyorganosiloxane-based and may include one or more of a variety of other components, such as certain coreactants, a maleimide component, a diluent component reactive at elevated temperature conditions, mono- or poly-hydroxyalkane components, and other components.
2. Brief Description of the Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, xe2x80x9cAnaerobic Adhesivesxe2x80x9d in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker. Inc., New York (1994) and references cited therein. Their uses are legion and new applications continue to be developed.
Anaerobic adhesive compositions may be classified as ones having high strength, medium strength or low strength. Controlling the strength of anaerobic adhesive compositions to render them having medium or low strength has ordinarily been achieved through the inclusion of a plasticizer or non-reactive diluent component into a high strength anaerobic adhesive composition, with the amount of such component influencing the degree of strength of the cured composition. While apparently satisfactory to provide an anaerobic adhesive composition with the properties desired, such an approach typically provides only a temporary solution to an immediate need and does little to advance the knowledge base of controlling the strength of anaerobic adhesive compositions.
Moreover, the inclusion of a non-reactive diluent in a high strength anaerobic adhesive composition by trapping the diluent in the polymeric matrix which forms upon curing, effectively limits the cross-link density which can form in the cured composition. This reduces the overall strength of the cured compositions.
More specifically, in use at ambient temperature conditions, the cured composition retains the non-reactive diluent. However, as the temperature of the environment in which the cured composition increases, the non-reactive diluent either evaporates or otherwise escapes from the polymeric matrix due to its decreased viscosity in view of the increased temperature. In either event, at increased temperatures (e.g., about 250xc2x0 F. and greater) the so-formed polymeric matrix becomes little more than a shell resulting in virtually no strength retention.
The patent literature points out examples of related anaerobic adhesives:
U.S. Pat. No. 4,107,109 (Kassal) (composition for making graft copolymers under anaerobic conditions at elevated temperatures, including a solution of certain uncured elastomers in a polymerizable vinyl monomer and a thermally activatable modified peroxide initiator, which form a continuous phase with the resulting vinyl polymer forming a separate and discrete phase); U.S. Pat. No. 4,216,134 (Brenner) (one-component anaerobic adhesive compositions which include ethylenically unsaturated diluent monomers, prepolymers and triallyl cyanurate or triallyl isocyanurate as reaction components); U.S. Pat. No. 4,269,953 (Brand) (certain biphenylene additives as reactive plasticizers which are said to render easier working, molding, extruding and the like, of the polymer and react to cross link certain aromatic thermoplastic polymers); U.S. Pat. No. 4,302,570 (Werber) (the purported use of reactive non-terminal hydroxydiesters of unsaturated organic dicarboxylic acids or anhydrides as plasticizers for anaerobic adhesives); U.S. Pat. No. 4,384,101 (Kovacs) (thermosetting resin mixtures which contain epoxide components, isocyanate components, latent-hardening components and triallyl cyanurate as a cross-linking compound); U.S. Pat. No. 4,431,787 (Werber) (polymerizable acrylic monomers, depicted with internal chain unsaturation as well as acrylic unsaturation, which cross-polymerize through the sites of internal chain unsaturation to furnish the reaction product); U.S. Pat. No. 4,524,176 (Pike) (anaerobic adhesive which includes the reaction product of an hydroxyl-containing polyester and a glycidyl acrylate) and the addition of a modifierxe2x80x94i.e., triallyl cyanuratexe2x80x94to alter flexibility and bond strength of the cured adhesive); U.S. Pat. No. 4,600,738 (Lamm) and U.S. Pat. No. 4,624,725 (Lamm) (two-component acrylic modified polyester adhesives of (a) the acrylic modified polyester reaction product of a glycidyl acrylate and a hydroxyl containing polyester and (b) an organometallic acid salt containing a polymerizable monomer).
Also of interest are:
U.S. Pat. No. 5,567,741 (Casey) (in the context of foaming applications, acrylate anaerobic compositions, certain of which include ethylene glycol); U.S. Pat. No. 3,794,610 (Bachmann) (plasticized anaerobic compositions including a polymerizable acrylate ester monomer (a non-silicone based acrylate monomer), a peroxy polymerization initiator and a polymeric plasticizer); U.S. Pat. No. 4,267,330 (Rich) (certain diaza accelerators for curable adhesive and sealant compositions); U.S. Pat. No. 3,988,299 (Malofsky) (heat curable composition having improved thermal properties, which includes certain acrylate monomers and maleimide compounds); and U.S. Pat. No. 5,302,679 (Maandi) (anaerobic compositions which expand when post cured).
In addition, L. J. Baccei and B. M. Malofsky, xe2x80x9cAnaerobic Adhesives Containing Maleimides Having Improved Thermal Resistancexe2x80x9d in Adhesive Chemicals, 589-601, L-H, Lee, ed., Plenum Publishing Corp. (1984) reports the use of maleimidesxe2x80x94specifically, N-phenyl maleimide, m-phenylene dimaleimide and a reaction product of methylene dianiline and methylene dianiline bismaleimidexe2x80x94to increase the thermal resistance of anaerobic adhesives which are fully cured at temperatures of at least 150xc2x0 C.
And, F. J. Campbell, xe2x80x9cElectron Beam Curing Improves High Temperature Strength of Vinyl Ester Adhesivesxe2x80x9d, Nat""l SAMPE Symp. Exh., 59-63 (1977) speaks to radiation curing of acrylic-modified epoxies together in formulations with vinyl functional monomers (i.e., divinyl benzene, trialkyl cyanurate and styrene) to form cured resins of higher level (cross-linking and superior ambient and elevated temperature performance.
Silicones (or polyorganosiloxanes), because of their excellent thermal stability, have been used for many sealant, adhesive and coating applications. However, because of large amounts of dissolved oxygen and high permeability to oxygen, conventional wisdom generally believed until recently that silicones would not be anaerobically curable.
For instance, U.S. Pat. No. 4,035,355 (Baney) teaches anaerobically curing sealant compositions of acrylate-containing polyorganosiloxanes and a hydroperoxy polymerization initiator. These compositions require relatively long cure timesxe2x80x94i.e., about 24 hoursxe2x80x94and therefore would have limited commercial acceptance.
U.S. Pat. No. 5,391,593 (Inoue) is directed to a silicone rubber sealant composition of an organopolysiloxane, organic peroxide and carbon black which is said to cure under anaerobic conditions into silicone rubber having improved physical properties. These silicones require about 2 to 3 days after removal of oxygen to fully cure. Such a cure profile again would meet with poor commercial acceptance.
Japanese Patent Document JP 04-268,315 appears to be directed to an anaerobically and ultraviolet curable polyorganosiloxane composition for adhesive purposes that is reported to have good heat resistance.
Recently, Loctite Corporation made an advance in the field of anaerobically-curable silicone formulations by teaching an anaerobic composition including (a) a silicone fluid formed as the reaction product of a first silane having at least one hydrolyzable functional group, and a second silane having a (meth)acrylic functional group and at least one hydrolyzable functional group; (b) a (meth)acrylate monomer; and (c) polymerization initiator. See U.S. Pat. No. 5,605,999 (Chu). These anaerobically-curable silicone formulations are referred to herein as xe2x80x9cSiMAxe2x80x9d.
While appealing for many commercial applications, certain other commercial applications requiring enhanced resistance to thermal degradation at elevated temperature conditionsxe2x80x94such as, machinery operations or operations which ordinarily occur at elevated temperature conditions, for instance, oil field applications or applications in electric motorsxe2x80x94, may be better served by a composition demonstrating a resistance and degradation profile more precisely tailored to that application.
Accordingly, it would be desirable to provide an anaerobically curing silicone composition, which cures in a short period of time without sacrificing heat stability and strength properties of the cured resin, and which demonstrates enhanced resistance to thermal degradation at elevated temperature conditions. It would further be desirable to be able to control the strength of the cured resin while maintaining high temperature resistance.
Notwithstanding the state-of-the-technology, a one-part, anaerobic adhesive composition would be desirable which is capable of curing under ambient environmental conditions, and which, when cured into reaction products, demonstrates superior properties, such as controlled strength and superior resistance to thermal degradation at elevated temperatures.
The present invention meets the desires discussed above by providing methods of controlling the strength of high temperature resistant anaerobic adhesives through the use of certain additives. That is, the present invention provides anaerobic adhesive compositions, reaction products of which demonstrate controlled strength at ambient temperature conditions and enhanced resistance to thermal degradation at elevated temperature conditions.
In one aspect of the invention, the compositions include (a) a (meth)acrylate component; (b) a coreactant; and (c) an anaerobic cure-inducing component. Such compositions may also include (d) a maleimide component.
In another aspect of the present invention, the compositions include (a) a (meth)acrylate component; (b) a maleimide component; (c) a diluent component reactive at elevated temperature conditions; and (d) an anaerobic cure-inducing component. Such compositions may also include a mono- or poly-hydroxyalkane component, a polymeric plasticizer component, and/or a chelator.
In yet another aspect of the invention, the compositions include: (a) a SiMA; (b) a (meth)acrylate component; (c) a maleimide component; and (d) an anaerobic cure-inducing component.
In this aspect of the invention, such compositions may also include alternatively, or in addition, to the maleimide component, a mono- or poly-hydroxyalkane component, a polymeric plasticizer component, and/or a chelator.
In still another aspect of the invention, the compositions include: (a) SiMA; (b) a (meth)acrylate component; (c) a mono- or poly-hydroxyalkane component; and (d) an anaerobic cure-inducing composition.
In yet still another aspect of the invention, the compositions include: (a) a SiMA; (b) a polymeric plasticizer component; and (c) an anaerobic cure-inducing component.
In this aspect of the invention, such compositions may also include a (meth)acrylate component, a mono- or poly-hydroxyalkane component, and/or a chelator.
The invention also provides a process for preparing reaction products from the anaerobic adhesive compositions of the various aspects of the present invention, the steps of which include applying the composition to a desired substrate surface and exposing the coated substrate surface to conditions which are appropriate to effect cure thereofxe2x80x94e.g., exposure to conditions in which air is substantially excluded therefrom.
Also, the invention of course provides the reaction products so-formed by the above-described process, which reaction products demonstrate superior thermal properties such as resistance to degradation at elevated temperatures.
The present invention will be more fully appreciated by a reading of the detailed description and the illustrative examples which follow thereafter.
As noted above, the present invention is directed to anaerobic adhesive compositions which are based on a (meth)acrylate component and/or SiMA component, together with an anaerobic cure-inducing composition.
The (meth)acrylate monomer suitable for use in the present invention may be chosen from a wide variety of materials represented by H2Cxe2x95x90CGCO2R1, where G may be hydrogen, halogen or alkyl of 1 to about 4 carbon atoms, and R1 may be selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, aralkyl or aryl groups of 1 to about 16 carbon atoms, any of which may be optionally substituted or interrupted as the case may be with silane, silicon, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, carbamate, amine, amide, sulfur, sulfonate, sulfone and the like.
(Meth)acrylate monomers suitable for use herein include polyethylene glycol di(meth)acrylates, tetrahydrofuran (meth)acrylates and di(meth)acrylates, hydroxypropyl (meth)acrylate (xe2x80x9cHPMAxe2x80x9d), hexanediol di(meth)acrylate, trimethylol propane tri(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate (xe2x80x9cTRIEGMAxe2x80x9d), tetraethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, di-(pentamethylene glycol) di(meth)acrylate, tetraethylene diglycol di(meth)acrylate, diglycerol tetra(meth)acrylate, tetramethylene di(meth)acrylate, ethylene dimethacrylate, neopentyl glycol diacrylate, trimethylol propane triacrylate and bisphenol-A di(meth)acrylates, such as ethoxylated bisphenol-A (meth)acrylate (xe2x80x9cEPIBMAxe2x80x9d).
More specific (meth)acrylate monomers particularly desirable for use herein include polyethylene glycol di(meth)acrylates, bisphenol-A di(meth)acrylates, such as EBIPMA and tetrahydrofuran (meth)acrylates and di(meth)acrylates, hydroxypropyl (meth)acrylate, hexanediol di(meth)acrylate, trimethylol propane tri(meth)acrylate, a (meth)acrylate ester corresponding to the structure as shown below: 
where
R2 may be selected from hydrogen, alkyl of 1 to about 4 carbon atoms, hydroxyalkyl of 1 to about 4 carbon atoms or 
R3 may be selected from hydrogen, halogen, and alkyl of 1 to about 4 carbon atoms;
R4 may be selected from hydrogen, hydroxy and 
m is an integer equal to at least 1, e.g., from 1 to about 8 or higher, for instance, from 1 to about 4;
n is an integer equal to at least 1, e.g., 1 to about 20 or more; and
v is 0 or 1.
Of course, combinations of these (meth)acrylate monomers may also be used.
When used, the (meth)acrylate monomer should be present in the compositions within the range of from about 1 percent by weight to about 60 percent by weight, desirably from about 5 percent by weight to about 50 percent by weight, such as from about 10 percent by weight to about 40 percent by weight, based on the total composition.
SiMA, such as taught by and claimed in U.S. Pat. No. 5,605,999 (Chu), the disclosure of which is hereby expressly incorporated herein by reference, may be used instead of or in addition to the (meth)acrylate monomer as the anaerobically curing resin. That is, such silicone fluids may be formed as reaction products of (a) a silane material within the formula RnSi(X)4xe2x88x92n, where R is H, C1-12 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl and derivatives thereof, and monovalent ethylenically unsaturated radicals, X is a hydrolyzable functionality and n is an integer from 0 to 3, and (b) a silane material within the formula Rxe2x80x2mRpSi(X)4xe2x88x92(m+p), where Rxe2x80x2 is a (meth)acrylic functional group, R and X are as above, and m is an integer from 1 to 3 and m+p is an integer from 1 to 3. Certain of these moieties ordinarily may be reaction products of halogenated trialkyl silanes, tetraalkoxysilanes and (meth)acrylic-subtituted trialkoxysilanes.
In the reaction forming SiMA, the first silane should be used in an amount with the range of from about 1 to about 99 mole %, desirably from about 30 to about 90 mole %, such as from about 50 to about 85 mole % of the combination of the first and second silanes. The second silane should be used in an amount with the range of from about 1 to about 99 mole %, desirably from about 15 to about 70 mole %, such as from about 20 to about 50 mole % of the combination of the first and the second silanes. Often, third and fourth silanes are used to prepare SiMA.
In the compositions of the present invention, the hydrolyzable functionality in either or both of the first silane or the second silane may be any functionality which, when attached to a silicon atom through a Sixe2x80x94O, Si-halo, Sixe2x80x94N or Sixe2x80x94S bond, is readily hydrolyzable in the presence of water. Examples of such functionalities include, but are not limited to, halogen, (meth)acryloxy, alkoxy, aryloxy, isocyanato, amino, acetoxy, oximinoxy, aminoxy, amidato and alkenyloxy.
In the compositions of the present invention, R may be chosen from C1-C12 alkyl and C6-C12 aryl. In such instances when R is C1-C12 alkyl or C6-C12 aryl, examples of the first silane include, but are not limited to, dimethylchlorosilane, phenyltrichlorosilane, tetrachlorosilane, trimethylchlorosilane, trimethylmethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane and tetraethoxysilane.
When R2 on the second silane is chosen from C1-C12 alkyl, C6-C12 aryl, alkenyl, (meth)acryloxy and vinyl, the second silane itself may be (meth)acryloxypropyl trimethoxysilane, (meth)acryloxypropyl trichlorosilane, (meth)acryloxypropyl dimethylchloro silane, (meth)acryloxymethyl dichlorosilane and (meth)acryloxymethyldimethyl acryloxysilane.
The second silane component may ordinarily be obtained commercially or prepared by methods well-known in field of methacrylate-functionalized silanes. Examples of such methods may be found in U.S. Pat. No. 2,793,223 (Merker); U.S. Pat. No. 2,898,361 (Barnes, Jr.); U.S. Pat. No. 2,922,806 (Merker); U.S. Pat. No. 2,922,807 (Merker); U.S. Pat. No. 4,348,454 (Eckberg); U.S. Pat. No. 4,665,147 (Lien); U.S. Pat. No. 5,179,134 (Chu); U.S. Pat. No. 5,182,315 (Chu); and 5,212,211 (Welch, II), the disclosures of each of which are hereby expressly incorporated herein by reference.
Of course, appropriate combinations of first silanes may be used as the first silane component; likewise appropriate combinations of second silanes may be used as the second silane component.
When present, the SiMA (a) should be present in the composition in an amount within the range of from about 40 to about 95 percent by weight of the composition, and desirably from about 50 to about 90 percent by weight of the composition, such as from about 60 to about 85 percent by weight of the composition.
The anaerobic cure-inducing composition useful in the present invention includes a variety of components, such as amines (including amine oxides, sulfonamides and triazines). A desirable composition to induce cure in accordance with the present invention includes saccharin, toluidines, such as N,N-diethyl-p-toluidine and N,N-dimethyl-o-toluidine, acetyl phenylhydrazine, and maleic acid. Of course, other materials known to induce anaerobic cure may also be included or substituted therefor. See e.g., Loctite U.S. Pat. No. 3,218,305 (Krieble), U.S. Pat. No. 4,180,640 (Melody), U.S. Pat. No. 4,287,330 (Rich) and U.S. Pat. No. 4,321,349 (Rich). Quinones, such as napthoquinone and anthraquinone, may also be included to scavenge free radicals which form.
In one aspect of the invention, the compositions further include a certain coreactant. These compositions may also include a maleimide component.
When used, the coreactant may be selected from monomers within structures I and II, which are represented as: 
where X is present at least once on structure I (i.e., mono-, di- or tri-substituted) and itself may be chosen from H or DA, where D is attached to the ring and may be chosen from O, S or NH, and A is attached to D and is represented by structure III below: 
where Z represents a point of unsaturation, such as (a) a double bond with a second H being attached to C1 and an H or halogen being attached to C2, or (b) a triple bond;
E may be H; and alkyl, alkenyl, alkynyl, alkoxy, each of which may be linear, branched or cyclic, and aryl groups, having from 1 to about 20 carbon atoms, with or without substitution by halogen, silicon, hydroxy, nitrile, ester, amide or sulfate, provided that additional point(s) of unsaturation or heteroatoms, if any, in the groups represented by R (described below) are not alpha to Z; and
R may be H; and alkyl, alkenyl, alkynyl, alkoxy, each of which may be linear, branched or cyclic, and aryl groups, having from 1 to about 20 carbon atoms, with or without substitution by halogen, silicon, hydroxy, nitrile, ester, amide or sulfate; and
X1 is present at least once on structure II (i.e., mono-, di- or tri-substituted) and itself may be chosed from H or 
xe2x80x83where D and A are as defined above.
More specific examples of structures I and II, therefore, include structures III and IV, respectively, as depicted below: 
With respect to structure V below, D and A are present at least once and are also present together attached to ring atoms which are in alpha-beta relation to one another, as is depicted in the structure 
Of the coreactants represented above, particularly desirable ones are represented below by structures VI [triallyl cyanurate (xe2x80x9cTACxe2x80x9d)], VII [triallyl trimesate (xe2x80x9cTATxe2x80x9d)], and VIII [triallyl isocyanurate (xe2x80x9cTAIxe2x80x9d)] as follows: 
In addition, the coreactant may be a polymerizable substituted phenolic material, such as materials within structure IX as represented below: 
where A is as defined above and n is from 0 to about 5.
A particularly desirable choice of coreactant within structure IX is represented below by structure X: 
where n is from 0 to about 5 and which is commercially available under the trade designation xe2x80x9cTHERMAXxe2x80x9d SH-150AR from Mitsubishi Petrochemical Co., Ltd., New York, N.Y.
Other coreactants suitable for use herein include those within structures XI and XII, as shown below. 
where X is as recited above.
Of course, appropriate combinations of these coreactants may also be employed herein.
When used, the coreactant should be present in an amount within the range of about 1 to about 30 percent by weight, based on the total weight of the composition.
Many maleimide compounds are suitable for use herein as the maleimide component.
The maleimide component may include any maleimide which remains substantially unreacted at ambient temperature, but becomes reactive at increased temperatures approaching about 325xc2x0 F. and greater. Accordingly, many maleimide compounds are suitable for use herein as the maleimide component.
Generally, maleimides which are useful herein conform to the following structures: 
where R5 and R6 are selected from alkyl, aryl [such as phenyl (mono and polyphenyl) and derivatives thereof, such as nitro, hydroxyl, alkyl and the like], cycloalkyl, aralkyl and alkaryl groups, which should ordinarily contain from about 6 to about 100 carbon atoms, with about 6 to about 50 carbon atoms being desirable, any of which may be optionally substituted or interrupted as the case may be with silane, silicone, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, carbamate, sulfur, sulfonate, sulfone and the like. For instance, R6 may represent groups such as 
where the phenyl groups are substituted at one or more positions with linear, branched or cyclic alkyl, alkenyl, alkynyl, alkoxy, or aryl groups having from 1 to about 20 carbon atoms, with or without substitution by halogen, hydroxy, nitrile, ester, amide or sulfate; and Y may represent O, S, carbonyl, sulfone, or primary or secondary methylene groups substituted with linear, branched or cyclic alkyl, alkenyl, alkynyl, alkoxy, or aryl groups having from 1 to about 20 carbon atoms, with or without substitution by halogen, hydroxy, nitrile, ester, amide or sulfate.
Desirable maleimides include compounds within structures XIII and XIV shown below as structures XVII [N-phenyl maleimide (xe2x80x9cNPMxe2x80x9d)], XX [N,Nxe2x80x2-m-phenylene bismaleimide (xe2x80x9cHVA-2xe2x80x9d, commercially available from E. I. DuPont Chemical Co., Wilmington, Delaware)], XIX [N,Nxe2x80x2-(4,4xe2x80x2-methylene diphenylene)bismaleimide (xe2x80x9cBMI-30xe2x80x9d)], XX [N,Nxe2x80x2-(2,2xe2x80x2-diethyl-6,6xe2x80x2-dimethyl-4,4xe2x80x2-methylene diphenylene) bismaleimide (xe2x80x9cBMI-70xe2x80x9d or xe2x80x9cMB-7000xe2x80x9d, commercially available under the xe2x80x9cTHERMAXxe2x80x9d tradename from Mitsubishi Petrochemical Co., K-I Chemical Industry Co., Ltd., Tokyo, Japan)], XXI [2,2xe2x80x2-bis[4-(4xe2x80x2-maleimidediphenoxy)pheny]propane (xe2x80x9cMB-8000xe2x80x9d, commercially available under the xe2x80x9cTHERMAXxe2x80x9d tradename from Mitsubishi), and XXII [multi-functional maleimide prepared as a condensate of aniline, o-toluidine and terephthaldehyde with maleic anhydride, (xe2x80x9cMP-2000Xxe2x80x9d), commercially available under the xe2x80x9cTHERMAXxe2x80x9d tradename from Mitsubishi]: 
where R7 may be selected from H or alkyl (such as CH3), and n is an integer within the range of 1 to about 10.
The maleimide component should be present in the composition in an amount within the range of from about 5% to about 20%, based on the total weight of the composition.
The compositions may also include a diluent component reactive at elevated temperature conditions.
Reactive diluents include those materials which are particularly (1) unreactive at ambient temperature conditions and (2) reactive at elevated temperature conditions. In addition, such diluents should be capable of not only reacting with other components of the inventive adhesive compositions, but also with reactive moities on itself. This feature allows the diluent to self-polymerize as well as polymerize with reactive moities on the other components of the composition. As such, the reactive diluent becomes incorporated into the polymeric matrix which forms at ambient temperature and which further forms at increased temperatures. The incorporation of the reactive diluent provides at least in part for the high temperature performance demonstrated by the cured composition.
More specific examples of such reactive diluents include alkenyl- or alkynyl-terminated silicone fluids, such as vinyl- or allyl-terminated silicone fluids, an example of which is vinyl-terminated polydimethyl siloxane.
Other examples of reactive diluents based on silicone fluids include alkenyl- or alkynyl-terminated MQ resins. MQ resins are a family of silicone-based materials with a structure represented generally by (R3SiO1/2)x(SiO4/2)y. Ordinarily, the ratio of x to y is in the range of about 0.5 to about 1.0 and R is alkyl, such as methyl; however, a portion of the total R content may also include hydrogen, other alkyl, alkenyl, alkynyl, aryl or derivatives thereof. Where a portion of a the total R content includes vinyl, functionality in the form of vinyl-dimethyl-SiO1/2, vinyl-methyl-SiO2/2 and/or vinyl-SiO3/2 may be present, and the resulting resin is termed by the art skilled as a vinyl-MQ resin.
Vinyl-MQ resins may ordinarily be prepared by (1) acidifying water-soluble sodium silicate, and thereafter capping the resulting sol with a trimethylsilyl group as well as with vinyl-containing silane or (2) co-hydrolyzing and/or co-condensing silanes containing trimethylsilane groups, vinyl silane groups and tetraoxysilane. For a further discussion of commercial silicone resins of this type, see R. H. Blaney et al., xe2x80x9cSisesquioxanesxe2x80x9d, Chem. Rev., 95, 1409-30 (1995).
Still other examples of the reactive diluent include alkenyl-terminated cyclosiloxanes, such as vinyl- or allyl-terminated cyclosiloxanes, desirably 2,4,6-trimethyl-2,4,6-trivinyl-cyclotrisiloxane (xe2x80x9cvinyl-D3xe2x80x9d) or 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane (xe2x80x9cvinyl-D4xe2x80x9d). In addition, alkynyl-terminated cyclosiloxanes may also be used herein.
And of course appropriate combinations of such reactive diluents may be used.
When used, the reactive diluent should be employed in an amount within the range of about 1 to about 50 percent by weight, based on the total weight of the composition.
The compositions may also include a mono- or poly-hydroxyalkane component.
The mono- or poly-hydroxyalkanes include alkylene glycols, like ethylene glycol, propylene glycols and propane triols, butane glycols and butane triols, butane tetraols, butylene pentaols and the like, pentylene glycols and pentane triols, pentane tetraols, pentane pentaols, pentane hexaols and the like, hexylene glycols and hexane triols, hexane tetraols, hexane tetraols, hexane pentaols, hexane hexaols, hexane heptaols and the like, and combinations thereof, may be used, as noted above. Such hydroxyalkanes tend to increase the cure speed, improve the shelf-life stability and improve the surface insensitivity (i.e., improve the bonding strength on oiled and/or slow curing substrates, such as zinc substrates) of anaerobic formulations in which they are placed, and decrease the break strength of reaction products of such formulations without compromising the prevailing torque thereof.
When used, the mono- or poly-hydroxyalkanes should be employed in an amount within the range of from about 0.01 to about 10 percent by weight, based on the total weight of the composition.
In certain other compositions of this invention, a polymeric plasticizer component may also be in included. The polymeric plasticizer should aid in bond formation and bond strength on insensitive, unreactive and slow-to-cure metal substrate surfaces, such as zinc and re-oiled surfaces.
The plasticizer component may be chosen from a wide variety of plasticizers depending on the desired properties of the composition and/or reaction product thereof. See e.g., U.S. Pat. No. 3,794,610 (Bachmann), the disclosure of which is hereby expressly incorporated herein by reference.
A particularly desirable plasticizer for use herein is a polymeric plasticizer, such as one available commercially under the tradename xe2x80x9cUNIFLEXxe2x80x9d 300 from Unicamp Corporation, Jacksonville, Fla. xe2x80x9cUNIFLEXxe2x80x9d 300 is a medium molecular weight polymeric plasticizer (made from hexanedioic acid and polymer with 1,4-butane diol and 1,2-propane diol), which is liquid at 25xc2x0 C. whose viscosity at that temperature is 3300 cps. This polymeric plasticizer is reported to be resistant to high temperatures.
When the compositions are to be applied on zinc, stainless steel or re-oiled substrates, a poly(ethylene glycol) monooleate, such as poly(ethylene glycol) 200 monooleate, may be used in this regard as well.
When used in the inventive compositions, a high strength formulation results which is particularly well-suited for use as a sealant.
When present, such plasticizers may ordinarily be used in the compositions in an amount within the range of from about 1 to about 20 percent by weight, such as about 1 to about 6 percent by weight, based on the total weight of the composition.
A chelator is ordinarily included in an amount sufficient to control shelf-life stability of the composition.
Appropriate chelators may be chosen from a variety of materials, such as ehtylenediamine tetraacetic acid (xe2x80x9cEDTAxe2x80x9d) and diethylene triamine pentaacetic acid pentasodium salt (xe2x80x9cDTPAxe2x80x9d).
Chelators are ordinarily used in the compositions in an amount from about 0.001 percent by weight to about 0.06 percent by weight, based on the total weight of the composition.
The inventive compositions may also include other components, such as free radical initiators, free radical accelerators, inhibitors of free radical generation, as well as metal catalysts.
A number of well-known initiators of free radical polymerization may be incorporated into compositions of the present invention including, without limitation, hydroperoxides, such as cumene hydroperoxide (xe2x80x9cCHPxe2x80x9d), para-menthane hydroperoxide, t-butyl hydroperoxide (xe2x80x9cTBHxe2x80x9d) and t-butyl perbenzoate.
Such peroxide compounds may be employed in the present invention in the range of from about 0.1 to about 10 percent by weight of the total composition, with about 0.5 to about 5 percent by weight being desirable.
Stabilizers and inhibitors (such as phenols including hydroquinone and quinones) may also be employed to control and prevent premature peroxide decomposition and polymerization of the composition of the present invention.
Accelerators may be employed to enhance the rate of cure propagation, such as in amounts in the range of about 0.1 to about 5, such as about 1 to about 3, percent by weight of the total composition. When the accelerator is in the form of a metal catalyst solution or a pre-mix, it may be used in an amount in the range of about 0.03 to about 0.1% by weight of the total composition. Other agents such as thickeners, plasticizers, fillers, and other well-known additives may be incorporated in the inventive composition where the art-skilled person believes it would be desirable to do so.
The compositions of the present invention may be prepared using conventional methods which are well known to those persons of skill in the art. For instance, the components of the inventive compositions may be mixed together in any convenient order consistent with the roles and functions the components are to perform in the compositions. Conventional mixing techniques using known apparatus may be employed.
The compositions of this invention may be applied to a variety of substrates to perform with the desired benefits and advantages described herein. For instance, appropriate substrates may be constructed from steel, brass, aluminum, zinc and other metals and alloys, ceramics and thermosets.
The compositions of this invention may also be used to impregnate the pores of substrates constructed from such materials.
Such uses of anaerobic compositions generally as impregnant sealants is well-known. Indeed, Loctite Corporation has for many years sold impregnant sealants under the trademark xe2x80x9cRESINOLxe2x80x9d, such as xe2x80x9cRESINOL RTCxe2x80x9d and xe2x80x9cRESINOL 90Cxe2x80x9d.
The inventive compositions, when used as impregnant sealants, may be formulated to have high temperature resistance when cured or low viscosity so as to be curable more quickly and to have enhanced shelf-life stability over existing commercial impregnant sealants.
For those impregnant sealants to be used in high temperature applications, a coreactant (such as TAC or TAI) should be present in an amount within the range of about 20 to about 30 weight percent.
For those lower viscosity impregnant sealants formulated for faster cure speed and enhanced shelf-life stability, a mono- or poly-hydroxyalkane component should be present in an amount within the range of about 1 to about 10 weight percent.
In addition to imparting lower viscosity, faster cure speeds and enhanced sealant formulations, the use of mono- or poly-hydroyalkanes as a component of impregnant sealants aids in the aqueous wash out of uncured compositions from the porous part to be sealed.
The compositions of this invention cure as their name connotes under anaerobic conditions. Nevertheless, other cure modalities may also be employed, if desired, provided of course appropriate choices are made for the components of the inventive compositions to render them curable under the desired conditions. For instance, see the ""305, ""640, ""330 and ""349 patents.
As with other anaerobic adhesives, the compositions of the present invention are capable of curing in the substantial absence of air. However, unlike some anaerobic adhesive compositions, the compositions of this invention are capable of curing to form a reaction product at ambient environmental conditions, i.e., at room temperature, instead of requiring elevated temperatures. The requirement of elevated temperatures for curing such adhesives increases manufacturing costs due at least in part to increased energy consumption. The so-formed reaction product forms an acceptable bond without requiring a second part primer material, such as is described in the ""738 and ""725 patents supra. Thus, the inventive compositions are one-part compositions. And the requirement of a second part primer to form an acceptable bond adhesive increases manufacturing costs due at least in part to the required additional material and is also disadvantageous at least in part with respect to lacking the convenience of a one part system.
The invention also provides a process for preparing a reaction product from the anaerobic adhesive composition of the present invention, the steps of which include applying the composition to a desired substrate surface and excluding air from the environment in which the substrate is positiond.
In another aspect of this invention, there is provided a method of producing anaerobically curing SiMA-containing compositions.
Initially, when SiMA is to be present in the inventive compositions, the following method represents a method for its preparation. The method of preparing SiMA includes the step of allowing at least one first silane to react with at least one second silane in the presence an effective amount of water to hydrolyze hydrolyzable groups on the first and second silanes, thereby producing a silicone fluid. The first silane is within the formula, RnSi(X)4xe2x88x92n, where the R groups may the same or different and selected from hydrogen, C1-C12 alkyl, C6-C12 aryl, C7-C18 arylalkyl, C7-C18 alkylaryl and monovalent ethylenically unsaturated radicals excluding (meth)acryloxy functional groups, X is a hydrolyzable functionality, and n is an integer of from 0 to 3. The second silane is within the formula, R1nR2mSi(X)4xe2x88x92(m+n), where R1 is a (meth)acryloxy functional group and R2 is selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-C12 alkyl, C6-C12 aryl, C7-C18 arylalkyl, and C7-C18, alkylaryl, X is a hydrolyzable functionality, m is an integer from 1 to 3, and m+p is an integer from 1 to 3.
At ambient temperature and in the presence of oxygen, additional components are next added. For instance, the (meth)acrylate component, maleimide component and an anaerobic cure-inducing component (and if desired any of the other components noted above) are thereafter added to SiMA, thereby producing an anaerobically curable composition in accordance with this invention, which when cured demonstrates high strength and resistance to thermal degradation at elevated temperatures.
The composition may be positioned onto, and in contact with, the surfaces by any suitable means such as spreading or dipping and the surfaces then brought into close proximity. Any solvent which may be present should be allowed to evaporate before the surfaces are brought into close proximity. Alternately, when the composition shows sufficient fluidity, the surfaces can be brought into close proximity and the composition subsequently positioned, e.g., by capillary action, into the small volume between, and in contact with, the surface. The composition however positioned and enclosed by the surface, being effectively excluded from oxygen, cures to an insoluble solid and adheres to the surface, thereby providing an assembly with two or more surfaces held in a fixed relative configuration.
In view of the above description of the present invention, it is clear that a wide range of practical opportunities is provided.